The cataleptogenic antipsychotic drugs, haloperidol and chlorpromazine increased the turnover rate of acetylcholine in the nucleus caudatus and nucleus accumbens whereas the noncataleptogenic antipsychotic drug clozapine had no effect on the turnover rate of acetylcholine. Both types of antipsychotic drugs decreased the turnover rate of acetylcholine in the globus pallidus. Tolerance to the effects in the three nuclei developed with chronic administration of each of the three drugs. The antidepressant drugs had no consistent effect on acetylcholine turnover. Desipramine and chlorimipramine decreased turnover in the striatum and hippocampus. Tolerance developed to the effects of desipramine after chronic treatment. Iprindole increased the turnover rate in the hippocampus. Nomifensine increased the turnover rate of acetylcholine in the cortex, hippocampus and diencephalon, as did amphetamine. Amitriptyline had no effect on the turnover rate of acetylcholine in the areas studied. BIBLIOGRAPHIC REFERENCES: Cheney, D.L., Zsilla, G. and Costa,E.: Acetylcholine turnover rate in n. accumbens, n. caudatus, globus pallidus and substantia nigra: Action of cataleptogenic and noncataleptogenic antipsychotics. In Costa, E. and Gessa, G.L. (Eds.): Advances in Biochemical Psychopharmacology. Vol. 16, New York, Raven Press, 1977, pp. 179-186. Robinson, S., Cheney, D.L., Moroni, F. and Costa, E.: Acetylcholine turnover in brain nuclei of rats injected with various antidepressnats. In Proc. of a symposium on "Depressive Disorders", held in Rome, Italy, May 1977, in press.